It has been found that phenolic resin, such as phenol-formaldehyde resins may be cured more quickly by the use of alkylene carbonates such as ethylene carbonate.
The use of alkylene carbonates as hardeners for phenolic resins permits attainment of a shorter gelling time and thus a quicker curing as well as an improved resistance to hot water of the wood materials produced therewith. This latter important property which is a parameter of weather resistance, determined by measuring tensile strength V 100, perpendicular to plate. *(See German Industrial Standards (DIN) No. 68 761, sheet 3). * FNT Tensile strength V 100 means pretreatment of the test specimen by storing the same for 2 hrs. in boiling water whereas Tensile strength means non-pretreatment of said test specimen.
Unfortunately, the use of alkylene carbonates as hardeners raises certain difficulties when used with phenol aldehyde resin solutions. Although the alkylene carbonates may be readily processed after addition to the phenol aldehyde resin solutions, incorporation of alkylene carbonates into the phenolic resin binder solution raises certain difficulties. For instance, if one adds solid alkylene carbonate to the phenolic resin binder solution, this would raise difficulties since the curing takes place almost immediately during the step of dissolving, thus undesirably forming small solid particles. But, even when the alkylene carbonates is added as a liquid, colloidal particles are formed, if one does not provide for an instantaneous and complete mixing; and this is attained only with great technical difficulties if at all. The solid and colloidal particles so formed are responsible for considerable breakdowns during manufacture of wood materials, due to the blockage of the nozzles in the spraying system by means of which the liquids are added to the solid components of the wood material.
The precipitation of the colloidal particles may only be avoided by adding the alkylene carbonate in very dilute solution to the binder solution. But if the diluting agent is water, this would mean adding an unfavourably large amount of water to the wood material during spraying with the binder solution. This is disadvantageous because inter alia the water can dissolve only 20 per cent by weight of e.g. propylene carbonate; and the large amounts of water require respectively more evaporation heat and longer moulding time.
It is an object of this invention to overcome these difficulties arising by using alkylene carbonates as the hardeners for phenol aldehyde resin binder solutions. Other objects will be apparent to those skilled in the art from inspection of the follosing description.